Alloy



Patented Aug. 16, 1932 UNITED, STATES PATENT "OFFICE GEORGE P. HALLIWEL, OF WILKINSBURG, PENNSYLVANIA, ASSIONOB TO WESTING- HOUSE ELECTRIC 8: EANUFACTUBING COMPANY, A CORPORATION OF PENNSYL- VANIA No Drawing.

I u" the alloy to a simple heat treatment for from 12 to 36 hours.

Alloys containing copper, manganese and a nickel are extensively utilized as resistors in electrical apparatus, they being especially a suitable for this purpose because they have an abnormally high specific resistance. Furthermore, alloys of thls type do not deteriorate from rust orexposure to the atmosphere and, when the proportions of the ingredients of the alloys are maintained within certain limits,their electrical and hysical properties are both permanent and re 'able.

I have made the discovery that the roportiona'l limit and tensile strength of a1 oys containing manganese, nickel and copper may be considerably increased by a suitable heat treatment. The heat treatment increases the brittleness of the alloys but, for.

some purposes, ductility is not highly essential. For example, when it is not necessary to work the alloy after it is subjected to my improved process, high ductility may be sac-- rificed to some extent in obtaining an alloy having a high proportional elastic limit and a high ultimate tensile strength.

In practicing my invention,'the alloy is first cold worked, for instance, by cold rolling or by drawing it through a suitable die. It is then subjected to an ageing process at temperatures ranging up to 500 The preferred range of heat treatment, however, is between 300 C. and 450 C. At a temperature of 300 (3., about 24 hours are required to produce the maximum increase in mechanical strength while, if the temperature is inarmor Application filed November 21, 1928. Serial No. 408,938.

creased to 450 0., the maximum increase in mechanical strength may be obtained in approximately12 hours.

A greater maximum hardness may be obtamed by heating at a lower temperature for a-Jlonger period of time but good results are obtained at temperatures up to 450, and the time of treatment necessary to secure the maximum hardness may be correspondingly decreased When the alloy is heated above 450, however, the maximum hardness that may be obtained decreases rapidly until, at

temperatures above 500' (3., it is practically ne ligible hile my invention is capable of increasing the mechanical properties of copper, nickel and manganese alloys in any proportion, I prefer to apply the treatment to alloys containing 10% to copper, 60% to 10% nickel, and 10% to 40% manganese because alloys having a higher percentage of commercial manganese have thetendency to become brittle and unworkable.

The following specific example will explain my process, although it will be understood that the example is to be considered as an illustration and not as a limitationof my invention. 1 i

A wire composed of an alloy, consisting of 52.3% nickel, 19.8% copper and 27.3% manganese, was first drawn through a suitable ie by means of which its cross sectional area was reduced about 35%. It was then heated, at a temperature of 350 C., for 24 hours in vacuum, whereupon it was allowed to cool to room temperature.

As the result of the foregoing heat treatment, the proportional elasticlimit of the alloy was increased from 70,000 to 183,000 pounds per square inch and itsultimate tensile strength was increased from 162,000 pounds to 245,000 pounds per square inch. In general, copper-nickel-manganese alloys, having proportions within the'ranges abovespecified which have been subjected .to my improved heat treatment, have a proportional limit of 140,000 to 225,000 poundsper square inch and an ultimate tensile strength of 200,-

000 to'300,000 ounds per s uare inch.

The reason or the marke increase in the mechanical properties of the alloy is not clear- I understood. It is believed, however, that,

during the heat treatment, a solid solution of one or more of the metals, a compound re- 5 sulting from the chemical combinatlon of one of the metals with an impurity which is present, or a compound of two or more of the ingredients or impurities of the alloy, precipitate out in the form of very fine particles of 1 submicroscopic size which increase the hardness of the alloy. I do not desire, however,

to limit my invention to any particular theory that now prevails or may be later advanced.

The term manganese refers to the prodnot known as commercial manganese which,

at the present stage of the metallurgical art, contains about 95% of manganese. Other ele- 1.

ments present include about 1.7% iron and about 1.5% silicon. It is apparent that all of my alloys contain the latter elements in amounts proportional to the nominal content of manganese and such proportional impurities will be understood herein in all instances where the contents of manganese is specified.

2:5 Although I have described certain specific embodiments of my invention, other modifications will be apparent to those skilled in the art. For example, the heat treatment may be conducted in a fused salt bath, such as a mixture of potassium and sodium nitrates or it may even be conducted in air. It is, therefore, desired that only such limitations shall be imposed upon my invention as are indicated by the appended claim.

I claim as my invention:

The process of increasing the mechanical properties of electric resistance alloys consisting essentially of about 20% copper, about 50% nickel and about 30% manganese which comprises cold workingand then subjecting them to a heat treatment at 300 to 450 C. for from 12 to 24: hours.

In testimony whereof, I have hereunto subscribed my name this 15th day of November,

' GEO. P. HALLIWELL. 

